Ballast apparatus with dimming control



May 28, 1963 E. J. HUBERTY 3,091,720

BALLAST APPARATUS WITH DIMMING CONTROL Filed July 3, 1961 3 Sheets-Sheet 1 dI- 06g] :{Ia/ /25 2/ ,edu *26- I@ C-i i 476% 4( 215 i -47 T6 K13 5,12 .f IA fmrmfwl -fmsnmmf* Tj *1 -'P /52 m -s jf 7:2 21 5.1 c? 20N fofA f 32 W20 l u .36 I 1 Zw 1| Z219 1 Mu VPU R5 l 71a/ 7111 342 L V y, y l nsf-i 8 d 22 5-2 @n e f C 0 j 120 Vous Ac. (50 f', '/55 'L/ I/ s l .54 I G lg 552,5, M+

cg Ew/maya May 28, 1963 E. J. HUBERTY 3,091,720

BALLAST APPARATUS wrm DIMMING CONTROL Filed July 3. 1961 5 Sheets-Sheet 2 .3. gig pbs-1,1111 .52 74' $2, F2 o ti IU May 28, 1963 E. Jl HUBERTY BALLAST APPARATUS WITH DIMMING CONTROL Filed July s. 1961 iii 3 Sheets-Sheet 3 'ISU '300 United States Patent Omce 3,091,720 Patented May 28, 1963 3,091,720 BALLAST APPARATUS WITH DIMMING CONTROL Elmer J. Huberty, Chicago, lll., assigner to Advance ill'rransformer Co., Chicago, Ill., a corporation of mois Filed July 3, 1961, Ser. No. 121,414 22 Claims. (Cl. 31598) This invention relates generally to devices which are farmharly known as ballasts and more particularly is concerned with the construction of a ballast which is intended for use with gaseous discharge lamps for lightmg purposes and which has a novel dimming control structure.

The gaseous discharge device inherently is a constant potential device which requires a certain voltage to ionize the gases therein `and a certain other voltage, substantially lesser in value, to maintain .the same ionized. At lower than the required ignition voltages the device will not ignite, and at lower than the required operating voltages the device normally will ybecome extinguished.

The problems which are involved in the construction of Vapparatus with which this invention is concerned are several in nature. Some of these are characteristic of all `apparatus for igniting and operating gaseous discharge devices, and certain other problems are related only to the particular functions desired of ballasts which include dimming control means.

The basic requirements of most gaseous discharge ballasts are to provide the necessary igniting and operating voltages from a source of A.C. voltage of relatively lower value than either the igniting or operating voltage, to ballast the device after its gas has ionized, that is, the lamp has ignited to prevent excessive ow of current from causing the latmp to destroy itself, and to do these eiciently and economically and without the need for complex and involved structures and circuits. Additional requirements may be posed by virtue of the requirements of certain circuits, the use of certain kinds of gaseous discharge devices and the like. For example, certain vapparatus may be required to operate at high power factor, certain kinds of lamps require filament windings in the transformers serving same and continuous flow of current in the filaments, and the like.

The value of lighting with vari-able intensity is not the concern of this invention, but, that there are important advantages to the control of the amount of light achieved from a given source will be denied by noue. The fac-t remain-s Vthat the specifications of a great many lighting installations, both residential and commercial, require manual (and sometimes automatic) control of the intensity of illumination. This invention is concerned with the construction of ballast apparatus which provides this control for rfhlorescen-t lamps.

The additional requirement for Ithe dimming control, as this form of variation is known, for gaseous discharge lamps is primarily to be able to achieve the full range of variation of lighting intensity without cancelling the ordinary functions built into a given ballast. Ideally, a dimming ballast should be able to start land operate at any condition of light output so that the user may turn ot the apparatus while it is at low intensity without being required to re-set the dimming control, knowing that when next he energizes the apparatus it will start reliably; a dimming ballast should be able to operate at lthe lowest intensity without tiickering either continually or intermittently; a. dimming ballast should be able to operate a-t all intensities without an unusual increase in temperature, without radical changes in the power factor; anda dimming ballast should have all of these attributes without being expensive and complicated to build and install.

Prior to this invention, dimming ballasts for lluorescent lighting did not meet the requirements set forth above. Even the most basic of requirements were ditlicult, if not impossible to achieve.

This invention has as its principal object, the achievement, not only of the basic requirements of dimimiug ballasts set forth above, but, as well, of all of the ideal requirements set forth above. This is accomplished on the basis of certain structures which will be described.

`In achieving a structure which will enable full dimming control of fluorescent lamps over a wide range of brilliance with reliability in starting and maintaining operation, the invention uses an improvement over prior structures which may `be termed a peaking circuit to superimpose a high voltage peak upon each half-cycle of the voltage which normally would be applied to the gaseous discharge device. Since the effect upon the R.M.S. voltage applied to |the liuorescent lamp is not changed effectively by this high peak, the `brilliance of the lamp likewise is not affected, although 4ignition at all values of R.M.S. is ensured for each half-cycle. It should be remelmbered that the actual gaseous discharge within a fluorescent lamp is extinguished between half cycles, the retention of illumination apparent to the human eye being caused by the uorescing of the phosphors coating the inside of the fluorescent tubes.

The ordinary dimming circuit uses an autotransformer connected with a variable output transformer, the variable output transformer being interposed between the primary and second-ary of the autotransformer to supply a variable voltage in series with the secondary winding. The R.M.S. and peak voltages applied to the lamp vary directly with the variation in the voltage tapped olf the variable transformer. By peak voltage here it is ntended to describe a peaking of a sont that is often found in the wave form of high leakage reactance transformers of the type desirable for the lluorescent lamps ordinarily used in dimming circuits. Since the peak voltage determines whether the lamp will re-ignite between halfcycle extinguishment obviously the minimum value of peak voltage limits the range of usefulness of a given device. It has been found that the condition of pearl: voltage at which the lamp no longer will reliably re-ignite in known `ballasts is one in which the R.M.S. of the lamp voltage, and hence its brilliance, is quite high. A

The invention, therefore, provides a structure in which the peak voltage of the voltage wave applied to the lamp is substantially independent of changes in the R.M.S. voltage, or at least decreases at a rate substantially less than the rate at which the R.M.S. voltage decreases, so that the lamp may be dimmed to a condition of extremely low brilliance before its re-igniting characteristics are affected adversely. This property is directly concerned .also with the ability of the lamp to be ignited at low intensities of brilliance, after once having been fully extinguished.

The invention contemplates, among other things, a novel magnetic structure for a peaking transformer which will accomplish the desired functions outlined above, and additionally circuit details which will complement the magnetic structure. Two of these details should be considered most important and fundamental to the invention, and they are means tor causing the pulse produced by the peaking circuit to be superimposed upon a ringing signal of frequency substantially higher than the line frequency; and means for suppressing the R.M.S. voltage increase which would be produced in the peaking circuit with increased differential between the lamp R.M.S. voltage and the peak voltage. The first mentioned phenomenon has been `found to give substantial improvement in the reliability of ignition of the fluorescent lamps at conditions of low lighting intensity.

One of the important disadvantages of prior structures which has been eliminated by the invention is that where a group of lamps is used together the lower limit of dimming is the light intensity at which the first lamp fails to reignite. The peak voltage required to re-ignite a lluorescent lamp varies from lamp to lamp. Since the intensity of the lamps is still rather high compared to the condition of no light at all, in ordinary dimming circuits the extinguishment of one of several lamps usually results in a substantial sudden decrease in illumination which is annoying :and undesirable. The invention enables the light intensity of a plurality of lamps to be decreased almost to complete extinguishment without the extinguishment of any one of them.

The use of complicated and expensive circuitry perhaps may provide some solution to the problems mentioned, but it is believed that even through the use of such apparatus, the important objects of `the invention have not been achieve-d in prior structures. It is therefore even more of an advance in the arts and sciences to achieve the salutary and desirable results of the invention with apparatus which is economical and simple. One result which has only been alluded to above, for example, is the elimination of flickering which has been found to occur in many prior ballast circuits at low intensity illumination. The structure herein has cornpletely eliminated all ilickering at all useful intensities while rendering the ignition of the lamps substantially more dependable.

A preferred embodiment of the invention has been constructed and successfully operated over an extended range of intensities, using a so-called rapid start uorescent lamp. The rapid start `lamp is one in which the lamp is provided with filaments that are heated at all times, which therefore provides a reliable and continuous source of electrons for aiding ignition and reignition of the lamp. The starting and operating voltages of these fluorescent lamps are substantially lower than uorescent lamps such as the so-called instant start lamps. The specification and drawings describe the apparatus in considerable detail, but only by way of example and not limitation. For example, the structure readily may be adapted to igniting and operating two or more lamps, and these lamps need not be of the rapid start structure, but preferably should be.

In the drawings:

PIG. l is a `circuit diagram of a ballast circuit using the construction of the invention herein, shown applied to the ignition and operation of a single gaseous discharge lamp which has filaments in its envelope.

FIG. 2 is a semi-diagrammatic view of the .so-called peaking transformer, the same being a top plan view of the same with portions in section to show the contours of the magnetic core thereof.

FIG. 3 is a view similar `to that of FIG. 2 but of the ballasting transformer.

FIGS. 4a, 4b, 5a, 5b, 6a, 6b, 7a, 7b, 8a and 8b are graphs of the voltage across the terminals T-2 and T-6 under open circuit condition, with the brush of the variable transformer in different locations, for the condition (a) of the ringing condenser not in circuit, and (b) the ringing condenser in `the circuit.

FIGS. 9a and 9b are graphs of voltage across the secondary winding S-S with and without the condenser C-2 in circuit.

The basi-c invention comprises an improvement upon known ballasting apparatus with dimming control for operating fluorescent lamps, and especially such apparatus for use in operating fluorescent lamps at high power factor. The known apparatus for operating a single lamp comprises a high leakage reactance transformer provided with a primary winding and secondary winding, separated by a magnetic shunt. These two windings are connected in autotransformer relationship across a fluorescent lamp. The preferred lamp is the rapid start lamp which has a heated filament that carries current continuously because `such lamps will remain ignited for very substantial reductions in operating voltage and are more easily reignited than instant start lamps, for example.

To achieve the dimming control, instead of providing a direct connection between the primary and secondary, the prior apparatus included a variable transformer connected across the line in parallel with the primary and having a movable brush wiping taps or exposed points so that the total voltage of the variable transformer or portions thereof may be used to aid the secondary voltage to increase the total voltage available across the lamp, the lamp being unable to sustain itself with the voltage of the secondary alone. The terminal of the secondary winding opposite that connected to the lamp was connected to the brush of the variable transformer. This general structure is also characteristic of the invention herein also, but there are additional components which provide the substantial improvement.

As stated above, the improvement generally comprises the addition of a peaking circuit to provide a continuous peak of voltage superimposed upon the voltage applied to the lamp so that the re-ignition of the lamp is ensured for substantially all conditions of brilliance. Various means for providing peaking in gaseous discharge circuits are known, but in this invention the structure provided is not obvious for several reasons. Merely providing peaking will result in a constant peak superimposed upon the R.M.S. voltage and will provide additional R.M.S. voltage. Thus, undesirable instant starting of the rapid start lamps at low intensities will occur which shortens the life of the lamps by gradually destroying their filaments. Additionally, the added R.M.S. voltage permits the intensity of the lamp to be decreased materially, without materially decreasing the peak voltage, thus obviating the benets of peaking.

In the invention herein, the peaking occurs without any increase in R.M.S. voltage; the peak on the voltage wave is substantially constant regardless of the amplitude of the R.M.S. voltage; and it occurs with a ringing voltage wave that improves its reliability.

In FIG. 1 there is illustrated a circuit using the invention for the ignition, operation and control of intensity of a single rapid start lamp L having filaments 10 and 12 in the ends thereof. The fluorescent lamp ballast 14 is shown enclosed in a broken line block since these are components normally included in a single housing, such as a metal canister. The variable transformer 16 is shown enclosed in another broken line block, this normally being a separate component, commercially available in many different designs. The peaking means of the invention is designated 18 and is also shown enclosed in a broken line block since it can be separately manufactured also. The two blocks l14 and 18 are connected by the dotted lines 2t]` to indicate that the ballast 14 and the peaking circuit 18 conveniently may be included within a single canister and potted together. Under such circumstances, there will be six leads emerging from the canister. In the circuit there are shown the four lamp leads 22, 24, 26 and 28 the two primary leads 30 and 32; and the two peaking circuit leads 34 and 36. The leads 24 and 30 are common, and this is also true of the leads 32 and 36.

If the three components 14, 16 and 18 are made independently and are required to be connected up with the lamp L and the A.C. line by the installer, the ballast 14 will have the four lamp leads 22, 24, 26 and 28 emerging therefrom, along with the lead 32 and a sixth lead 38 which is to connect with the peaking circuit 18. The peaking circuit will have two leads 34 and 36 and a third lead which is to be connected to the lead 38 from the ballast 14. The variable transformer 16 will have only three leads extending Vtherefrom although from FIG. l it appears as though there are six. The conductors 4G and 42 are merely extensions of the leads 30 and 32 respectively, drawn only to render the diagram easier to follow, while the conductor 36 is actually connected to the lead 3-2 exterior of the housing of the variable transformer 16. The lead 34 connects with the wiper or brush 44 of the transformer.

Consider now the ballast circuit and the variable transformer circuit. The ballast circuit includes a transformer 46 ywhich is shown in physical embodiment in FIG. 3 mounting a primary winding P-l connected across the line at terminals 48 and 50 through the leads 30 and 32 and extensions 40 and 42 respectively. In the practical example the terminal 48 was at ground potential and the lead 40 was white, while the terminal 50 was the hot side and the lead 4t2 was black. This is a matter of choice in this case, however, since the connections could be reversed. T he starting aid to be provided by a metallic fixture mounting the lamp L, if desired, would have to take the polarity of the terminals 48 and 50 into consideration.

The primary winding P-1 has a closely coupled power factor secondary winding S-1 connected thereto at the terminal T-3, the right hand end of the secondary winding S-l being designated as the terminal T-4. There is also a closely coupled filament winding F-1 whose terminais are T-l and T-2, the latter being common with the left hand end of the primary Winding P-1. As a matter of fact, the three windings F-l, P-i and S-l normally are part of a continuous coil, with the various terminals brought out as taps. The leads 22 and 24 are connected to the terminals T-1 and T-Z to permit the filament Winding F-l to serve the filament and to connect the left hand terminal of the primary winding P-l to the left hand terminal lof the lamp L. The power factor condenser 'C-l is connected across the primary winding P-1 and secondary winding S-l from terminal T-2 to T-4. These connections are by way of example as the filament winding F-l may be included as part of the primary and the power factor correcting circuit of C-1.

The secondary winding S-2 and the filament winding F-2 are separated from the other windings of the transformer 46 by a shunt 52 so that the transformer 46 in effect is a high leakage transformer providing good ballasting for the iiow of current after the lamp L is ignited. If desired, the filament winding F-Z may be wound on top of the primary. The terminals of the windings S-Z and F-2 are T-S, T-6 and TJ. The leads 26 and 28 are connected to the terminals T-6 and T-T respectively, so that the filament Winding F-Z serves the right hand iilament 12, while the secondary winding S-2 has its right hand end connected to the right hand end of the lamp L. The left hand terminal T-S of the secondary winding S-Z is not connected directly to the primary winding P-1, but instead is connected through other intervening components. The lead 38 connects with this terminal T S.

There is provided a variable transformer 16 which comprises a winding P-2 connected across the line from terminal T-S to T-9 so that line voltage is applied thereto. The wiper or =brush 44 connects with the lead 34 and picks of a portion of the winding P-2 to the right of the brush which is used to oppose the voltage of the secondary winding S-2 and the primary P-1 and hence this right hand portion of the winding P-Z may be considered a secondary winding S-3. Its voltage obviously will vary from zero when the `brush is at terminal T-9 to line voltage when the brush is at terminal T-8. The instantaneous polarity of the variable transformer 16 is chosen to have a direction which is as shown by the arrow V-V alongside the winding P-2, and the instantaneous relationships of the other windings discussed thus far as shown by the arrows V--P for the primary voltage, and V-S for the voltage of the secondary winding S-Z. Note that if the brush 44 is at terminal T-9 the voltage across the lamp L is the vectorial sum of the voltages of P-1 and S-2, if we assume that the brush lead 34 is connected directly to the lead 38 as in prior structures. Since the arrows V-S and V-P are in the same direction, considering a loop circuit including the windings P-l and S-2 with the lamp, the numerical values of the voltages will be additive to a great extent, the degree depending upon the phase difference between windings.

As the brush 44 is moved to the left, the effective secondary winding S-3 becomes greater and greater in size, and the circuit which includes the primary winding P-1 and secondary winding 8 2 includes a greater portion of S-3 but with the opposite instantaneous voltage sense, and hence bucking the voltage V--S thereby decreasing the available RMS. voltage for the lamp L and hence decreasing the intensity of its light.

As thus far described the circuit is known. The addition ot the peaking circuit 18 completely changes the apparatus, not only because there is an added structure and added function, but also because the ordinary functions are substantially altered.

`Instead of connecting the brush 44 directly to the terminal T-S of the secondary winding S-2, the peaking circuit 18 is interposed. This comprises a transformer 54 having three windings thereon-a primary winding P-3, a secondary winding S-4 and a secondary winding S-S. The windings are connected electrically end to end providing the terminals T-10, T-ll, T-12 and T-IS, with the first two windings mentioned closely coupled, but with the third winding S-S separated from the other two by a magnetic shunt 56. The transformer S4 is illustrated in FIG. 2, and as will be seen there is an unusually large slot 58 punched in the core within the secondary winding S-S whose purpose is to provide very narrow saturable flux paths 60 so that a very narrow and high voltage peak will `be produced in a manner to be described. The terminals 'I2-10 and T-ll are connected respectively to the leads 3o and 34 so that the voltage which energizes the primary winding P-S is the voltage which is subtended in the effective secondary winding S-S by movement of the brush 44. The greater the voltage across the secondary winding S-3 the greater the voltage energizing the primary winding P-S and hence the greater the voltage peak which will be produced. lt will be seen, however, that the greater the voltage across the effective secondary winding S-3 the smaller the R.M.S. voltage available to the lamp L, and hence this arrangement provides a peak voltage which varies inversely as the amplitude of the R.M.S. voltage applied to the lamp. The winding S-4 is in autotransformer additive relationship with the primary winding P-S being connected therewith at terminal T-ll and closely coupled therewith. Actually, it is Wound in the same window of the transformer core as the primary winding P-3.

The secondary winding S-S of the transformer 54 is connected in autotransformer relationship with the primary winding P-3 and the additive secondary winding S- but is in voltage opposition to both of these. The arrows indicate this at V-PK, V-SK and V-SB. The instantaneous voltage sense of the secondary winding S-S is additive to the voltage V-S of the winding S-2 ibut. huclied by the voltage of the winding S-4. lf the circuit is traced `from the terminal T-6 to the terminal T-2, it will follow the path through the various windings: first through the secondary winding S-2 to terminal T15 and the lead 33 to the terminal T-13, through the secondary winding S-S additively to terminal T-12, through the winding S-4 bucking to the terminal TA1, through the lead 34 to the brush v44, through the secondary winding S-3 bucking to the terminal T-9, through lead 32 to the terminal T-3, through the primary winding P-l additively to the terminal T-2.

Obviously when the brush 44 is at terminal '119, there will be no primary voltage V-PK and none developed in the secondaries S-4 and S-5 except that which may be due to the passage of current resulting from the secondary S-2. There will be practically no peaking voltage, While the R.M.S. voltage for the lamp L will be maximum.

When the brush 44 is at terminal T-8, there will be maximum primary voltage across winding P-3 and a maximum of peaking voltage available, while the R.M.S. voltage available at the lamp L will be a minimum.

The peak voltage which will be described in some detail, is developed in the secondary winding S-S by virtue of the construction of the transformer 54, and this is what is desired, but there will also be some R.M.S. voltage developed in the winding S-S as well. The secondary winding S-4 being bucking will develop an R.M.S. voltage which tends to cancel the R.M.S. voltage developed in the winding S-S so that only the maximum of peak voltage is obtained from the peaking circuit l18. The function of the primary Winding P-3 is to develop the proper value of voltages in S-4 and S-5. The voltage V-PK has little or no effect upon the total voltage applied across the lamp L.

It will be noted that there is a capacitor C-2 connected across the secondary winding S-S from terminal T-12 to terminal T-13. This capacitor is chosen to tune the circuit to provide a ringing effect. The harmonic chosen is preferably above the fifth harmonic of the frequency of the line, such as for example, a frequency of 300 cycles per second. It has been found that this expedient sharpens the pulse and therefore provides additional extent to the controllable range of the apparatus. In other words, the dimming can carry the brilliance of the lamp to a lower value without losing the ability to re-ignite, and without flicker, if the ringing arrangement is used. Additionally, but of no lesser importance is the fact that the lamp is subjected to a repetition of high voltage pulses instead of one, and hence is more likely to ignite.

In order to demonstrate the manner in which the apparatus has `been found to operate, and without committing the invention to the theory of operation which may be used to explain the results, graphs of voltage wave shapes are illustrated in FIGS. 4 through 9.

In FIGS. 4 through 8 there are illustrated the open circuit voltages across the lamp L taken from the terminals T-Z to T-6, with the lamp out of the circuit. These voltage waves are such as would be encountered in a circuit which is designed for use with a rapid start T-lZ uorescent lamp of 40 watt rating. This lamp is commercially available and is well suited for use in dimming circuits because of the continuous flow of current in its filaments. Normally `it ignites at 250 volts, and operates at its rated current of 430| milliamperes with a requirement of about 105 volts R.M.S. to remain ignited.

Ignition and re-ignition of the lamp depends wholly upon the voltage initially applied thereto or applied between half cycles and hence the criterion of ignition is the peak voltage applied to the lamp. If a sufficient peak voltage is applied to the lamp, the lamp can operate at very low currents and hence at very low light intensities.

The invention herein is primarily concerned with the ignition of the lamp, and hence is intended to provide best conditions of peak voltage to enable the low intensities desired to be reached without extinguishment and without flickering. This is brought out in the voltage waves shown in FIGS. 4 through 8. The left hand portion a of each figure `is the voltage across the terminals T-Z and T-6 with the condenser C-Z not connected, While the right hand portion .b of each figure is the voltage across the same terminals but with the condenser C-Z in circuit as shown. These voltage wave shapes are substantially those which will appear on a cathode ray oscilloscope. The differences in the amplitudes and contigurations from figure to figure are due to the position of the brush 44.

In FIG. 4, the brush 44 is. disposed at the extreme left hand end of the variable transformer winding P-Z so that the minimum of R.M.S. voltage is available for operation of the lamp L when the lamp is connected but with a maximum of peaking voltage. The entire line voltage is across the primary winding P-3 to give the maximum of peaking effect from the secondary winding S-5. The peak produced is shown at 64 at an amplitude of Ep volts but in effect the voltage wave consists of a small sine wave indicated by the broken line at 66 of peak amplitude Es with the peak Em, superimposed thereon. The sine wave 66 is the voltage provided by the secondary winding S-Z and the peak `64 is provided by the peaking circuit 18. The analysis is not as simple as set forth, since there are probably other factors which enter, but the primary contributions are made by these two parts of the apparatus.

In FIGS. 5, 6, 7 and 8 the same voltage waves illustrated in FIG. 4 have been modified because of movement of the brush 44 to the right to different positions along the length of the variable transformer 16. In FIG. 5 the brush 44 is at about the 25% position along the winding, in FIG. 6 it is about half way, in FIG. 7 it is at approximately 75% of the way, and in FIG. 8 the brush 44 is at terminal T-9. It will be noted that the amplitude Em, of the peak portion 66 decreases from position to position until in FIG. 8 where the brush is at terminal T9 there is no voltage being applied to the primary winding P-3 and hence no peak is generated by the peaking circuit. The intermediate conditions result in a peak voltage which is dependent upon the position of the brush 44.

It will also be noted that movement of the brush 44 from terminal T-S to terminal T9 results in a gradual increase of the amplitude of the voltage wave provided by the ballast 14, and hence an increase in the R.M.S. voltage available for the lamp.

Most important, however, is the fact that the peak voltage Ep of the total voltage wave across the terminals T-2 and T-6 is practically the same in every case. The limiting oase is that of FIG. 8 where the peak voltage Ep and `the peak of the R.M.S. wave Es are substantially the same, and there is no detectable peaking effect.

In the actual circuit, the peak and R.M.S. voltages were measured at the following values:

Fig. Peak Ep RJLS.

In FIG. 9a there is illustnated the voltage wave of the voltage across the secondary winding S-S from terminal T-12 to T-13 with the condenser C-Z disconnected, and in FIG. 9b the same voltage is shown but with the condenser in place. The voltage in FIG. 9a is made up of a peak 64 superimposed upon a low amplitude sine wave of small R.M. S. value, but this R.M.S. voltage is actually bucked out by the secondary winding S-4 in the circuit so that it will not add to the R.M.S. voltage produced by the ballast 14 at low intensities of light. In actual values, the peak voltage Em, measured volts while the R.M.S. of the wave 68 measured 48 volts.

The above values are approximate, and are intended to emphasize the fact that the peak voltage of the wave applied to the lamp is quite substantial even at conditions of very 10W intensity, and as the R.M.S. voltage decreases the peak supplied by the peaking circuit increases and vice versa.

The invention contemplates the addition of the condenser C-Z in order to cause the peaking circuit to ring at a frequency which is several times the line frequency. As stated, this new frequency is preferably tive times or more the line frequency. The result of this ringing, which is a form of resonance, is that each pulse triggers the ringing circuit to produce a multiple pulse at every half cycle. This is seen in the modified form of the voltage wave of each of the figures at b. The resulting multiple pulses are of amplitudes including several that are higher than peak voltage otherwise would be. In the voltage wave of FIG. 4b for example, the peak voltage Ep was 35 volts higher than the peak Ep of FIG. 4a. This increased peak voltage was manifest in voltages produced at other positions of the brush as well, but as the peak produced by the peaking circuit 18 decreased, so did the excursions of the pulses caused by ringing as well as their amplitudes. In FIG. 5b for example, the peak voltage of the wave was the same as in FIG. 5a and the excursions of the ringing pulses were of no consequence. It should be appreciated. however, that this was a condition of dimming control in which the problem of ignition and reignition of the lamp was of no importance. The intensity of the lamp was substantially above the critical situations of very low intensity.

FIG. 9b is a voltage wave which shows the effect of the ringing circuit at maximum peaking voltage with the brush 44 at terminal T'S.

The measurements and wave shapes which have been discussed above have all been considered at open circuit, that is, with the lamp L out of the circuit. As mentioned previously, the lamp is essentially a constant potential device and is self-regulating, so that a decrease in the open circuit R.M.S. applied to the lamp will result in a decrease in the current flowing through the lamp. The lamp voltage will remain fairly constant, while the changes due to decrease in current will be compensated for by the reactive nature of the ballast to give the desired results.

Measurements were made of various parameters during operation of the lamp for different settings of the brush. At or quite close to the terminal T-S the lamp barely glowed and produced a minimum light output measured on a light meter with an arbitrary unit of l, while with the brush at terminal T8, the lamp glowed in full brilliance with the same meter giving a reading of 90 units. At the minimum setting, the current flowing through the lamp was 3.2 milliamperes, the peak voltage was 295 volts and the R.M.S. voltage was 135. At the maximum light setting, the current flowing through the lamp was 260 milliarnperes, the peak voltage had dropped to 186 volts and the R.M.S. voltage had dropped to 110 volts.

Between these two extremes, there were proportional The settings of the brushes as set forth above are the same approximately as they were for the settings of the figures identified. The lamp current was measured in the lead 38 in order to obtain the total flow, and is given in milliam-peres. The R.M.S. is the value across the lamp. The light was measured with a photoelectric cell connected across a galvanometer, and the units were those of the meter and are arbitrary. The peak voltages are not recorded since they varied considerably, but since these conditions are those of the lamp operating these readings would have no significance.

Attention is now invited to FIGS. 2 and 3. These show the transformers 54 and 46 respectively. The transformer 46 is not unusual in design, being merely a high leakage reactancc forced core type of structure.

The windings P-l, S-l and F-l are mounted on the left hand side in the window 70 upon the central winding leg 72. The windings 8 2 and F-Z are mounted in the right hand window 74 upon the central winding leg 72. The shunt 52 is formed by the inward projection 76 of the outer rectangular framing portion 78 and the outward extensions 80 of the central winding leg. These are juxtaposed and spaced apart to provide suitable nonmagnetic gaps at 82. In construction, the windings are pre-formed, are engaged over the central winding leg 72, and the resulting assembly is forced into the framing part 78 with the ends of the winding leg 72 matingly engaging the bridging yokes of the framing portion 78 at 84 and 86.

Variations in this construction are feasible. For example, the core may be formed of T and t. shaped parts held together with clamps.

Obviously the cores are formed of stacked steel laminations secured together as by rivets or the like.

The transformer 54 is of the same general physical construction as the transformer 46 in the respect that it is formed of stacked laminations of electrical steel, has a central winding leg 88, an outer framing part 90, windows 92 and 94 which mount the windings, the shunt 56 formed by extensions and projections and providing the gaps 96, and the mating engagement of the ends of the winding leg with the yokes. The important difference between the transformers, and for that matter between the transformer 54 and other transformers, is the presence of the large slot 58 at the particular position that it is located.

The dimensions of the core of the peaking transformer 54 may be studied to aid in an understanding of the operation thereof. The width of the central winding leg at K in the practical example illustrated was .831 inch. The width of the slot 58 was .721 inch indicated at l thereby leaving the narrow flux paths 60 on each side, having a width of .055 inch, indicated at M. This represents a reduction in width of the central winding leg of about 87%. Also the length of the slot 58 which is considered in the direction of the flow of primary llux through the central winding leg, is shown at N as l/2 inch, or about 60% of the width of the central winding The effect of the very narrow sections 66 is to cause the generation of a very high and narrow voltage peak due to the sudden saturation of the steel in these narrow sections. Upon saturation of the steel no voltage is generated in the secondary winding S-S because the length of the slot 58 is sufficient to inhibit any increase in iiux. The gene-ral proposti-ons used in the particular structure were found to be optimum, with no increase in length N being effective to improve the peaking. Decrease of this dimension from the 1/2 inch used was found to widen the peak pulse and add to the R.M.S. voltage generated in the secondary winding S-S. Moving the slot 58 away from the shunt 56 will :result in an increase in the R.M.S. voltage generated in the secondary winding S-S because of the increased opportunity for fringing of flux from fthe steel that is disposed between the slot 58 and the shunt 56. Obviously it is most advantageous to have as little steel between the shunt land fthe slot as practical and hence the end of the window 92 and ithc edge of .the slot 58 closest to the primary winding P-3 are substantially coincident.

The shunt 56 is of importance because it provides the return path for primary flux when the flux paths 60 are saturated; it provides the loose coupling between the primary P-S with its secondary S-4 `and Ithe secondary winding S-S to help regulate llow of current through the lamp L; it provides a high leakage reactance and hence an inductance which decreases the slze of condenser C-2 necessary to achieve the ringing resonance desired in the peaking circuit 18; and it prevents excessive exciting current in the primary which otherwise would occur with a satu- 1 l rating portion under the secondary winding S-5. Thus, the number of turns required to achieve a high peaking voltage is `less than otherwise would be needed.

The practical example which has been referred to herein was successfully operated without iiickering and with complete control and ease of re-ignition to light intensities of extremely low value. The physical characteristics of the apparatus are given hereinafter.

From the dimensions applied to the transformer 54, the proportional dimensions of it and the transformer 46 may be ascertained, since both `are drawn to the same scale. The overall length of the core of the transformer 54 was 4 inches, and its width slightly over 2 inches. The length of the core of transformer 46 was 5 inches and its width the same as the core of the transformer 54. This conveniently enabled both transformers `to be potted in a long narrow canister. The laminations were stamped from 24 gauge electrical steel and the transformer had a 1%: inch stack while the transformer 46 had a .625 inch The condenser C-1 was 3.7 microfarads with a rating of 230 volts A.C. and the condenser C-2 was .2 microfanad with `a 118 volt A.C. nating. The gaps 82 and 96 were .029 rand .01175 inch respectively.

The variable transformer was of a well known commercially available construction, designed to be connected tto a conventional 120 volt A.C. line and provide any de.- sired voltage between its brush 44 and one of its terminals within the range zero to 120.

lt is believed that the invention has been fully explained suiiiciently to be understood and applied by those skilled in this aint and it is desired to point out that variations can be made without in any way departing from the spirirt or scope tof the invention ias defined in the appended claims.

What it is desired to secure by Letters Patent of the United States is:

1. A device of the character described which includes a ballast for igniting and openating a gaseous discharge lamp adapted to be energized by a source o-f A.C. power and adapted to be connected with a variable output transformer, la peaking transformer connected with the ballast and `adapted to be connected with the variable output transformer, said ballast including a high leakage reactance transformer with first primary and first secondary windings loosely coupled and the windings having leads for connecting the `same to the said lamp, the peaking transformer including second primary and second secondary windings loosely coupled and with the second primary winding having leads for connecting same to be energized by the variable output transformer with a voltage that varies inversely as the voltage to be applied across the lamp, and with the second secondary winding having means for generating a peak therein and being connected in series with said first secondary winding and having an auto transformer connection with that lead of said ysecond primary winding adapted to be connected to the variable output transformer, whereby the peak amplitude generated in said second secondary will vary inversely as the R.M.S. voltage applied to said lamp.

2. Apparatus as claimed in claim l in which said peaking transformer has a third secondary winding closely coupled with the second primary winding and in voltage opposition to the second secondary winding to buck out the R.M.S. voltage developed in said second secondary winding.

3. Apparatus as claimed in claim 1 in which the second secondary is tuned to a frequency which is a multiple of the frequency of the A.C. source.

4. Means adapted for assuring the ignition of a fluorescent lamp at conditions of a low lamp current, the said means adapted to be associated and connected into an environment which includes an A.C. power source, a variable transformer `connected across the source and including an adjustable contact to be moved to different voltage output positions, a high :leakage reactance transformer having primary and secondary windings with the variable transformer output connected between the primary and secondary windings and arranged to provide a variable voltage bucking the voltage of the secondary depending upon the position of the contact, the primary and secondary windings being connected in auto-transformer relationship across the lamp, the first mentioned means including a voltage peaking transformer connected with the output of the variable transformer and arranged to superimpose a voltage peak upon the R.M.S. voltage applied across the lamp, the amplitude of said peak varying inversely with said R.M.S. voltage.

5. Means as claimed in claim 4 in which the peaking transformer is tuned to a multiple of the frequency of the source so as to provide a ringing voltage peak.

6. In a fluorescent lamp dimming circuit connected across an A.C. line and having a high leakage reactance transformer for providing an R.M.S. voltage across the lamp, a variable transformer for varying the R.M.S. voltage, and a peaking circuit for superimposing a voltage peak upon the R.M.S. voltage, means for multiplying the number of pulses provided by the peaking circuit.

7. A structure as claimed in claim 6 in which the means for multiplying the pulses comprises a ringing circuit built into said peaking circuit.

8. In a ballast apparatus with a dimming control for igniting and operating a iluorescent lamp at different light intensities `from `an A.C. source and which includes a high leakage reactance transformer connected to the lamp for applying an R.M.S. voltage to the lamp and a variable voltage output device connected to oppose the R.M.S. voltage applied to the lamp and having means for varying its output; a peaking circuit connected in circuit with said high leakage reactance transformer `for applying a peak of voltage superimposed upon said R.M.S. voltage to aid in igniting the lamp, said peaking circuit including a peaking transformer having a primary winding connected to be energized by the output of said variable voltage device so that the said primary winding is energized by output voltages which vary inversely as the R.M.S. voltage applied to said lamp, a peaking secondary winding loosely coupled to the primary winding and adapted to have the peak voltage generated therein, and a magnetic core mounting both the primary and secondary windings and having a large slot therein under the secondary winding to provide saturation at the voltage peaks of the `applied voltage to generate a sharp narrow voltage peak.

9. A peaking circuit as claimed in claim 8 in which there is another secondary winding on the core of said transformer, closely coupled with the primary winding and adapted to be connected in the lamp circuit bucking the peaking secondary winding to offset any R.M.S. voltage developed in said rst secondary winding.

10. A peaking circuit as claimed in claim 8 in which there is a condenser in circuit with said peaking secondary winding tuning same to a multiple of the said A.C. source to cause a ringing of said peak voltage.

l1. A peaking transformer for use in a fiuorescent lamp dimming circuit .and adapted to be connected to superimpose a peak voltage upon the R.M.S. voltage across the lamp, and the dimming circuit including a variable voltage device to change the R.M.S. voltage applied to the slamp, the peaking transformer comprising an elongate laminated iron core having an outer framing portion and a central winding leg, windings encircling the central winding leg and comprising a primary winding at one end of the leg and a secondary winding at the other end of the leg with a shunt disposed between the windings and having non-magnetic gaps therein, windows formed in the outer framing portion to accommodate said windings, the primary winding adapted to be connected to the variable voltalge device so that fit is energized in accordance with the voltage output of said device, the secondary winding adapted to be connected in the lamp circuit to the exclusion of the primary winding whereby the voltage generated in said secondary winding is adapted to be superimposed upon the R.M.S. voltage applied to the lamp, said central winding leg having a slot therein beneath the secondary winding and having its transverse edge closest to the shunt substantially coincident with the end of the secondary winding thereat, having a length along the central winding leg sufficient to prevent flux from being produced therein when the narrowed portion of the leg is saturated, and having a dimension transverse of the leg to cause fast ux saturation at the peaks of the applied voltage.

12. A peaking transformer as claimed in claim il in which the slot has dimensions to reduce the flux path through the central winding leg beneath the secondary winding by substantially more than tifty percent.

13. A peaking transformer as claimed in claim 11 in which the length of the rslot along the central winding leg is substantially more than fty percent of the width of said central win-ding leg.

14. A peaking transformer as claimed in claim 11 in which there is another secondary winding mounted in the same windows as the primary winding and adapted to be connected .in voltage opposition to the first secondary.

15. A peaking transformer as claimed in claim l1 in which there is a condenser tuning the said secondary to cause the peak produced by the said transformer to be a ringing one.

16. A dimming circiut for ballasting and controlling the operation of a fluorescent `lamp and the circuit adapted to `be connected across a source of A.C. power and a variable output voltage device having opposite end connector means for connecting the same across the source and having a lead connected to a brush which is variable so that positioning the brush along the exposed contacts of the variable voltage output device will provide a variable voltage from said lead to one or the other of the opposite end connector means, said circuit comprising, a ballasting transformer having a first primary winding and a iirst secondary winding loosely coupled one relative to the other and the first primary winding having means adapted for connecting the same across the source, one end of the first primary winding adapted to be connected lo a terminal of said lamp, a peaking transformer having a second primary winding and a loosely coupled peaking secondary winding and means for providing a sharp peak of vol-tage in said peaking secondary winding for each half cycle of voltage applied to the second primary winding, the second primary winding ladapted to be connected from said brush lead to the one of said end connector means, said one end connector means adapted to be connected to the second end of said first primary winding, one end of said rst secondary Iwinding adapted to be connected to the second terminal of said lamp and the second end of said rst secondary winding being connected in series with said peaking secondary winding and adapted to be connected in series with said brush, the two secondary windings `being additive when in circuit across said lamp with said rst primary winding, but that portion of the variable voltage device between said brush and said one end connector means adapted to be in voltage opposition to said two secondary windings, whereby decrease of I4 R.M.S. voltage which may occur across the lamp results in an increase in voltage applied to said second primary winding and hence in an increase in the peak voltage produced in said peaking secondary.

17. A dimming circuit as claimed in claim 16 in which Ithere is a third secondary winding closely coupled with said second primary winding and connected in series with said peaking secondary winding but in voltage opposition thereto whereby to compensate for R.M.S. voltage produced by said peaking secondary winding.

18. A dimming circuit as claimed in claim 16 in which there is a condenser tuning said peaking secondary winding to provide a series of pulses at each half cycle instead of a single peak.

19. Apparatus for use with a variable voltage device connected across a source of A.C. power for igniting and operating a gaseous discharge lamp with variations in intensity of light caused by adjustment of the variable voltage device to provide different voltages, and the voltage device including a brush movable to different tapped positions, the said apparatus comprising: a high leakage reactance transformer including at least a primary winding and a secondary winding and means for connecting the primary winding across the said source one side of the primary winding having means for connecting the winding to one terminal of said gaseous discharge lamp, means for connecting the second side of the secondary winding to the second terminal of the lamp, a connection to the second side of the secondary winding adapted to extend to the brush ofthe variable voltage device whereby when the primary and secondary windings are connected across the lamp, and the primary winding is connected acnoss the line, and the second side of the secondary winding is connected to said brush, the primary and secondary windings will be connected in autotransformer relation across the lamp but with the resulting voltage determined by the position of said brush, a peaking circuit in the connection of the second side of said secondary for superimposing a peak upon the R.M.S. voltage generated by said transformer to aid in starting the lamp, and having means for varying the amplitude of the peak inversely as the R.M.S. voltage produced due to changes of the position of the brush.

20. Apparatus as claimed in claim 19 in which the peaking circuit also has means for bucking out the R.M.S. voltage developed therein.

21. Apparatus as claimed in claim 19 in which a ringing circuit is provided in connection with said peaking circuit to render the peak a plurality of pulses.

22. Ballast apparatus for variably controlling the intensity of illumination from a fluorescent lamp energized by an alternating power source which comprises, a variable transformer having first and second terminals connected across said source and a variable tap positioned intermediate said terminals, a lamp ballast comprising a first primary winding, a rst secondary winding connected thereto and a second secondary winding, a magnetic core for said last named windings, said core having a magnetic shunt positioned between said first and second secondary windings, said primary winding being connected across said first and second variable transformer terminals, said primary winding and said second secondary winding each having one end terminal connected for energizing opposite electrodes of a iluorescent lamp, and in combination therewith, a peaking transformer having a second primary winding and third and fourth secondary windings all connected in series, a common core for said last three named windings, said last named fourth secondary winding being wound in opposing magnetic relation to said second primary winding and said third secondary winding, said core having a magnetically saturable reduced mag nctic cross-section dispose-d beneath said magnetically opposed fourth winding means connecting said second primary in series between said variable tap and said 15 second variable transformer terminal, means connecting said fourth winding with a free terminal of said second secondary winding, means connecting a common terminal of `said first primary and said first secondary with said second terminal, and means connecting the opposite terminals of said iirst primary and `secondary in operative relation, whereby a first energizing wave is applied to said first primary, said rst wave having an amplitude proportioned to the positioning of said tap between said term@ nais, and an inversely proportioned pulse is generated in said fourth primary winding for superposition on said iirst wave thereby to ignite said lamp.

References Cited in the file of this patent UNITED STATES PATENTS Notice of Adverse Deesion n Interference In Interferenc No. 94,236 involving Patent; N o. 3,091,720, E. J. Huberty, BALLAST APPARATUS WITH DIM MING CGNTROL, nal judgment adverse to the pa-tentee was rendered J an. 8, 1965, as to claim 19.

[Oficial Gazette Febr/amy 23, 1965.]

Disclaimer Chicago, Ill. BALLAST APPARATUS 3,091,7Q0.-E!mer J. Hubert VITH DIMMING ONTROL. Patent dated May Q8, 1963. Dlsclaimer filed Dec. 14, 1964, by the assignee,

Hereby enters this disclaimer to claim 19 of Suid patent.

[Ojeial Gazette Marr-h 30, 1.965.]

Advance Transformer 00. 

1. A DEVICE OF THE CHARACTER DESCRIBED WHICH INCLUDES A BALLAST FOR IGNITING AND OPERATING A GASEOUS DISCHARGE LAMP ADAPTED TO BE ENERGIZED BY A SOURCE OF A.C. POWER AND ADAPTED TO BE CONNECTED WITH A VARIABLE OUTPUT TRANSFORMER, A PEAKING TRANSFORMER CONNECTED WITH THE BALLAST AND ADAPTED TO BE CONNECTED WITH THE VARIABLE OUTPUT TRANSFORMER, SAID BALLAST INCLUDING A HIGH LEAKAGE REACTANCE TRANSFORMER WITH FIRST PRIMARY AND FIRST SECONDARY WINDINGS LOOSELY COUPLED AND THE WINDINGS HAVING LEADS FOR CONNECTING THE SAME TO THE SAID LAMP, THE PEAKING TRANSFORMER INCLUDING SECOND PRIMARY AND SECOND SECONDARY WINDINGS LOOSELY COUPLED AND WITH THE SECOND PRIMARY WINDING HAVING LEADS FOR CONNECTING SAME TO BE ENERGIZED BY THE VARIABLE OUTPUT TRANSFORMER WITH A VOLTAGE THAT VARIES INVERSELY AS THE VOLTAGE TO BE APPLIED ACROSS THE LAMP, AND WITH THE SECOND SECONDARY WINDING HAVING MEANS FOR GENERATING A PEAK THEREIN AND BEING CONNECTED IN SERIES WITH SAID FIRST SECONDARY WINDING AND HAVING AN AUTO TRANSFORMER CONNECTION WITH THAT LEAD OF SAID SECOND PRIMARY WINDING ADAPTED TO BE CONNECTED TO THE VARIABLE OUTPUT TRANSFORMER, WHEREBY THE PEAK AMPLITUDE GENERATED IN SAID SECOND SECONDARY WILL VARY INVERSELY AS THE R.M.S. VOLTAGE APPLIED TO SAID LAMP. 